Crystal Headphone A

• alternative name: Brush Electronics

This crystal headphone was produced by The Brush Development Co. Cleveland 14, Ohio, U.S.A, under license of American Telephone and Telegraph Company:  It was protected by several patents, namely in: U.S.A: 20,213; RE 20680; 1,995.257; 2,105.011; 2,106.143; 2,266.333. In UK: 318,934; 454,595; 573,687. In Canada: 1931; 1941.

There are two models: Type “A” and Type “B”: Type “A” Phones have an impedance of 50 kohms at 400 Hz  and have a wide range and uniform frequency response covering from 60 Hz to 10 000 Hz. Type “B” headphones are based in a light weight design (3 ½ ounce, for a pair of phones, half of the weight of Type “A”), built inside an aluminum hermetically sealed case, comfortable for radio operators, aircraft pilots, etc. Type “B” headphones have an impedance of 25 kohms at 400 Hz and their frequency response is similar to the Type A headphones (not so uniform).

Both Types “A” and “B” headphones may be used in a head band with a pair of phones or in a lorgnette handle using only a single phone.

This headphone here presented is a single phone used in several Brush equipment’s, sometimes as a headphone or as a microphone or in both  functions micro/headphone (as example  in the  Brush “Mail a Voice” Disk Recorder).

In questo link sono elencati 43 modelli, di cui 39 con immagini e 22 con schemi.
Elenco delle radio e altri apparecchi della Brush Development Co. / Clevite Electronic Components; Cleveland, Ohio